The present invention is related to a novel and improved process for the production of dehydrolinalyl acetate (DLA), which IUPAC name is acetic acid 1-ethynyl-1,5-dimethyl-hex-4-enyl ester, starting from dehydrolinalool (DLL), which IUPAC name is 3,7-dimethyloct-6-en-1-yn-3-ol, by acetylation.
Dehydrolinalyl acetate (compound of formula (I))
DLA can also be used in the production of linalylacetate (compound of formula (IV))
Nowadays, DLA is usually produced by an acetylation of DLL by using p-toluene sulfonic acid as an "organic-soluble" acid catalyst.
In course of this reaction significant amounts of side products, such as D,L-iso-3,7-dimethyl-7-octen-1-in-3-yl acetate (iso-DLA; compound of formula (V)),
The goal of the present invention was to find an improved process for the production of DLA, without the above mentioned disadvantages of the process of the prior art (especially reducing the amount of the side products).
Surprisingly it was found that in the absence of any catalyst, DLA is obtained by the acetylation of DLL with a significantly lower amount of undesired side products and with excellent selectivity and yield.
Therefore the present invention is related to the process of production of DLA, which is the compound of formula (I)
The process according to the present invention is usually carried out at elevated temperatures.
Preferably the process according to the present invention is carried out at a temperature of more than 50°C, preferably more than 80°C, more preferably more than 100°C
The process according to the present invention is preferably carried out at temperature of 100°C to 160°C.
DLL and acetic anhydride (Ac2O) can be added to the reaction mixture in equimolar amounts. It is also possible to use slight excess of either one of the compounds. Usually the acetic anhydride is used in an excess in regard to DLL.
The process according to the present invention is usually carried out without any solvent. But it would also be possible to use an inert solvent (or mixture of inert solvents).
Preferably the process according to the present invention is carried out without any solvents.
The starting material (compound of formula (II) and compound of formula (III)) can be mixed together before the process is started or one of the starting material can be added to the other while the process is going on.
Usually the compound of formula (II) is put into the reaction vessel and then the compound of formula (III) is added during a period of time.
After the addition and mixture of all the starting material the reaction mixture is let reacted for some time.
Usually the reaction time for the process according to the present invention is between 2 to 20 hours, preferably 2 - 18 hours, more preferably 2 - 15 hours.
At the end of the reaction, the remaining acetate anhydride and the acetic acid (product of the process) is removed from the reaction solution. This is usually done by distillation (normal pressure or at a reduced pressure).
The DLA which is obtained by the process according to the present invention can be used as such (flavour and fragrance applications) or it can be used in the production of other useful compounds, especially linanylacetate (obtained by hydrogenation of DLA).
The following examples serve to illustrate the invention. If not otherwise stated all parts are given are related to the weight and the temperature is given in °C
Into a 350 ml four necked round bottomed flask fitted with a thermometer and a reflux condenser 164.3 g DLL (1.06 mol) and 150 ml (1.6mol) Ac2O were added under stirring.
The yellowish reaction solution was heated to 110 °C (internal temperature). After 14 h. Afterwards the Ac2O and AcOH-mixture was distilled at 1,0 kPa (10 mbar) at 90 - 100 °C.
DLA was obtained in a yield of 70%.
The same reaction was repeated with an amount of 250ml Ac2O (reaction time 5 hours) and with an amount of 500ml Ac2O (reaction time 5 hours).
DLA was obtained in a yield 90% (250 ml Ac2O) and 94.2% (500 ml Ac2O).